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Keys to the Passivhaus standard: what is it and how to achieve it?

The Passivhaus standard is a voluntary energy certification standard for new and retrofitted buildings, aimed at providing maximum comfort for occupants, excellent indoor air quality and near-zero energy consumption.

Keys to the Passivhaus standard: what is it and how to achieve it?

The Passivhaus standard is a voluntary energy certification standard for new and retrofitted buildings, aimed at providing maximum comfort for occupants, excellent indoor air quality and near-zero energy consumption. It was developed in the 90’s by the Passivhaus Institute in Darmstadt Germany, and it has since been expanding across the globe. The current climate crisis is increasingly bringing the standard into the limelight due to its radical no-nonsense approach, rooted in buildings physics, a rigorous design process and an emphasis on proper site supervision and commissioning. The objective is to close the so-called “performance gap” (where buildings fail to perform as predicted), making them fit for purpose, comfortable, healthy, and resilient. A Passivhaus building typically consumes up to 90 % less energy than a conventional building.

This article, written by Oliver Style, explains some of the key aspects of the Passivhaus and what you need to do, to achieve certification.

Las claves de la certificación Passivhaus
Figure 1: Passivhaus certification plaque [Source: Álvaro Martínez]

Passivhaus: the Basic Principles

It is often said that the standard is based on the following 5 principles:

  • High levels of thermal insulation
  • High performance windows
  • Efficient mechanical ventilation with heat recovery
  • Air tightness
  • Absence of thermal bridges

Although this simplification can make it easier to understand what Passivhaus is all about, a Passivhaus building requires a holistic design process where the whole is more than the sum of the parts… and there are many parts. So, beyond the 5 basic principles, there are several other factors that are important for achieving certification and making sure a building does what it says on the tin, especially in warm climates, namely:

  • External shading devices to reduce solar gains and avoid summer overheating 
  • Efficient Domestic Hot Water (DHW) systems, equipment and lighting: to reduce primary energy consumption and reduce internal heat gains in summer (helping avoid summer overheating).
  • Efficient heating and cooling installations
  • In climates with sufficiently low minimum night time temperatures: Natural night ventilation combined with thermal inertia, to remove heat from the building without relying only on active cooling.
Figure 2: Global temperature change relative to 1850 - 1900 [Source: IPCC Special Report 2018]
Figure 2: Global temperature change relative to 1850 – 1900 [Source: IPCC Special Report 2018]

A building designed to have very low heat losses in winter, will also keep heat out in the summer: if you fill a vacuum flask with cold water in the summer, the water will stay cool for longer than if you just left it in outside in ambient warm air.  However, once the heat is inside, it will logically dissipate more slowly due to the high level of thermal protection. That is why it’s particularly important to go beyond the “5 principles” if you want to avoid overheating problems, which will increasingly become an issue as summers get warmer due to global warming (Figure 2).

Figure 3: Passivhaus certification criteria for new construction [Source: Passive House Institute 2016] [1]
Figure 3: Passivhaus certification criteria for new construction [Source: Passive House Institute 2016] [1]
Figure 4: Passivhaus certification classes [Source: Passive House Institute]
Figure 4: Passivhaus certification classes [Source: Passive House Institute]
Figure 5: Passivhaus Low Energy Demand certification criteria [Source: Passive House Institute 2016] [1]
Figure 5: Passivhaus Low Energy Demand certification criteria [Source: Passive House Institute 2016] [1]

PHPP: “Passive House Planning Package”

For the design of a Passivhaus building, the PHPP (“Passive House Planning Package”) tool is used, a quasi-steady-state single zone energy modelling program, based on a series of spreadsheets in Excel, that provides monthly and annual energy balances. The algorithms in the tool are based on a number of ISO standards, mainly in the monthly method of EN ISO 13790, now replaced by ISO 52016 0.

The PHPP has been calibrated with thermodynamic simulations carried on with the DYNBIL tool, developed by the Passivhaus Institute, itself calibrated by extensive validations with monitored data.

PHPP stands out for its simplicity compared to dynamic tools and can be used to model (albeit in a simplified way) a wide variety of active and passive systems, at a very affordable price. The results indicate the energy balance of the building in both summer and winter, yielding results of heating and cooling demands and total and final and primary energy consumption. Although a dynamic tool is- in principle- more accurate, the large number of parameters and input data increases the possibility of modelling errors and requires experience and time for accurate use. In energy simulation, it is sometimes better to be approximately correct than precisely wrong…

Passivhaus for new build

The Passivhaus standard for new buildings is performance based: i.e., it doesn’t limit thermal transmittance values ​​of the different construction elements, but establishes maximum energy demands and energy consumption, calculated with the PHPP. The air infiltration level cannot exceed 0,6 air changes per hour (ACH) at a pressure difference of 50 Pascals, measured with an on-site test, known as the “Blower Door” test.

The limiting values for heating and cooling demands and total primary energy consumption, are shown in Figure 3.

There are 3 classes of certification: Classic, Plus and Premium. Classic does not have renewable energy generation. To get to Plus, you have to generate ≥ 60 kWh/m2·a of renewable energy (references to the building’s footprint)- typically at least as much as what the building consumes. To reach Premium, the building must generate ≥ 120 kWh/m2·a (or 4-5 times more than what the building consumes). This is shown in Figure 4. The advantage of this approach is that energy demands are reduced first, before considering on-site generation of renewable energy. This differs from the conventional net-zero energy approach, which inevitably favours buildings with very large roofs on which a large solar PV generator can be installed, leading to buildings with a poor form factor (the ratio of enclosed envelope area to useful floor area), higher losses and where on-site renewable energy generation is prioritised over reducing energy use.

PHI Low Energy Building

If the above requirements are not met, a building can be certified as PHI Low Energy Building, complying with less stringent requirements, shown below in Figure 5.

Passivhaus for retrofitting: EnerPHit

For the retrofitting of existing buildings, there is the EnerPHit seal, which offers two ways to achieve certification:

  • EnerPHit, Demand Method: performance based, with the requirements shown in Figure 6
  • EnerPHit, Component Method: prescriptive, with the requirements shown in Figure 7

For both methods, an air tightness test result of N50 ≤ 1.0 ach must be obtained. The Classic, Plus and Premium classes are also applicable to the EnerPHit standard.

Figure 7: EnerPHit Certification Criteria, Component Method. [Source: Passive House Institute 2016] [1]
Figure 7: EnerPHit Certification Criteria, Component Method. [Source: Passive House Institute 2016] [1]
Figure 6: EnerPHit Certification Criteria, Demand Method. [Source: Passive House Institute 2016] [1]
Figure 6: EnerPHit Certification Criteria, Demand Method. [Source: Passive House Institute 2016] [1]

Overheating risk in summer

For certification, overheating risk is assessed through one of the two following methods:

  • With active cooling: the limiting total cooling demand must be met (sensible + dehumidification), calculated with the PHPP, with mechanical systems capable of maintaining thermal comfort at all times (according to ISO 7730), with an operating temperature ≤ 25 ºC and a maximum of 10% of the hours in the year with an absolute indoor humidity ≥ 12 g/kg dry air.
  • With passive cooling:  the maximum overheating frequency must be met, calculated with the PHPP, with a maximum of 10% of the hours in the year with an indoor operating temperature > 25 ºC.
Figure 8: Overheating frequency classification [Source: adapted by Jessica Grove-Smith, Passive House Institute]
Figure 9: Graph showing the modification of the summer temperature of the PHPP climate data, from the "Summer Temperature Tool"
Figure 9: Graph showing the modification of the summer temperature of the PHPP climate data, from the “Summer Temperature Tool”

In the case of passive cooling, it is important to stress that 10% of the hours of the year are a total of 876 hours with an indoor operative temperature above 25 °C (the whole month of August, for example). Therefore, the recommendation is not to exceed 5%, with a good design objective being 2 – 5%, shown in Figure 8.

To reduce the risk of overheating where no active cooling is available, it is important to perform stress tests of extreme climate situations with the PHPP. For this purpose, Jessica Grove-Smith of the Passivhaus Institute has developed theSummer temperature tool[2], which adjusts the summer temperatures in the PHPP climate file, taking into account the urban heat island effect and the increase in temperatures according to IPCC’s predictions (Figure 9). This feature will be integrated directly into PHPP version 10.

For tertiary buildings and/or buildings with areas exposed to very different indoor and outdoor conditions, it is advisable to accompany the PHPP calculation (a single zone tool) with a dynamic multi-zone calculation, to analyse specific zones that may be more susceptible to overheating (for example, the top floors in a tall building with west-facing glazing).

Additionally, if the building does not have an active cooling system, it is important to test assumptions regarding user behaviour, for example, in relation to closing blinds and opening windows at night for natural ventilation. Is it realistic to think that a person will sleep all night with the blinds open, all windows fully open, and all interior doors open? It is more likely that occupants will close the blinds before going to sleep so the sun light doesn’t wake them up in the morning. If you live in an urban area, you might want to close all windows facing the street to avoid noise. All this reduces natural night ventilation flow rates and the amount of heat that can be extracted from the building.

Although the goal is always to reduce dependence on active systems to maintain comfort, in most cases, some active cooling in summer is advisable. Fortunately, the summer is also the time when there is the most solar radiation, which means active cooling energy consumption can be directly off set with on-site renewable energy production.

Air tightness: the “Blower Door” test

Central to the Passivhaus standard is the “Blower Door” airtightness test, that measures air infiltration through a piece of equipment that pressurizes and depressurizes the building. Preliminary tests must be carried out before the interior finishes are completed (to detect and correct leaks, if found), together with a final test, according to the EN 13829 [3].

The “Blower Door” test is a clear indicator of build quality. What are the advantages of reducing air leaks?

  • Reduces energy losses and heating bills in the winter
  • Reduces the entrance of moisture in warm-humid climates, thereby reducing dehumidification cooling consumption and cooling energy bills
  • Improves comfort, eliminating air drafts
  • Improves people’s health by preventing the entry of radon gas, suspended particles and other pollutants from outside
Figura 8: Comparativa del nivel de infiltraciones requerido para Passivhaus, CTE y valores típicos para edificios existentes
Figure 10: Air infiltration levels required for Passivhaus compared with Spanish CTE and typical values for existing buildings

An air tightness strategy must always be accompanied by controlled mechanical ventilation, to ensure good air quality and the elimination of moisture and pollutants generated inside the building.

An existing building will typically have an infiltration level of n50 ~10 ach. A certified Passivhaus has an n50 ≤ 0.6 ach. The Spanish CTE Building Regulations, in the 2019 update, establishes a limit for air infiltration of n50 3 ach and 6 ach according to the compacity of the building (Figure 10).

Audits and certification: quality assurance from design to completed building

The certification process and auditing begin in the design phase and conclude when on-site construction is finished. Certification can only be carried out by the Passivhaus Institute or an approved Building Certifier. As an external agent to the project, the certifier verifies that the project complies with the standard and that construction has been completed as planned, accurately reflected in a the PHPP model. The client needs to supply detailed as-built architectural and service drawings, photographic documentation showing the execution of all elements related to energy and air tightness, the final certificate of the Blower Door test, the ventilation system commissioning results, together with a letter signed by the Site Supervisor, indicating that the project has been built as designed.

Passivhaus and health

Although the standard does not specify which materials you use in a building, the PHPP manual explicitly recommends the use of low-emission materials, to reduce VOC’s (volatile organic compounds) in indoor air.

To ensure good air quality, the correct sizing of the ventilation system at design stage is checked. Once installation is completed, the commissioning of the system and the measurement and adjustment of flow rates in all supply and return valves is mandatory.

The goal is to create healthy, comfortable, efficient and resilient buildings, closing the performance gap between projected and real-life performance.

Bibliography

  • [1] EN ISO 13790, Energy performance of buildings – Calculation of energy use for space heating and cooling. This standard has been revised by ISO 52016-1:2017
  • [2] Criteria for the Passivhaus, EnerPHit and PHI Low Energy Building Standard, version 9f. 15.08.2016 1/30. 2016 Passive House Institute.
  • [3] Passive House Institute Summer Temperature Tool, Available at: https://passiv.de/en/05_service/02_tools/02_tools.htm
  • [4] DIN-EN 13829, Thermal performance buildings – Determination of air permeability of buildings – Fan pressurization method. (ISO 9972:1996, modified).

Healthy home: materials and indoor air quality

The U.S. EPA (Environmental Protection Agency) estimates that the air in our homes is 2 to 5 times more polluted than outdoor air. After spending so much time at home during successive COVID lockdowns, the importance of living in a healthy home has perhaps become clearer than ever before.

Healthy home: materials and indoor air quality

Materiales y calidad del aire, claves para los espacios saludables
Figure 1: Example of materials that can affect a home’s indoor air quality [Source: Jose Hevia / H.A.U.S]

The U.S. EPA (Environmental Protection Agency) estimates that the air in our homes is 2 to 5 times more polluted than outdoor air. After spending so much time at home during successive COVID lockdowns, the importance of living in a healthy home has perhaps become clearer than ever before.

What kind of environmental conditions are we looking for in a healthy home? Operative or comfort temperatures of between 20 ºC – 25ºC, relative humidity between 40 % – 60%, and surface temperatures ≤ 3ºC of the indoor air temperature.  With an indoor air temperature of 20ºC and a relative humidity of 50%, interior surfaces need to be ≥ 13ºC to prevent the risk of mould growth, and ≥ 9ºC to avoid surface condensation. Exposure to mould spores can cause health issues such as eye, skin and throat irritation, nasal stuffiness, coughing and wheezing. Alongside healthy thermal conditions, good indoor air quality is key for wellbeing, solved largely by good ventilation, but also by preventing the entrance of outdoor contaminants (such as particulate matter, radon gas etc.) and by reducing the generation of indoor contaminants due to emissions from materials, furniture, and finishes.

If continuous and controlled ventilation is key, we need to get to the root of the problem: to reduce and avoid materials that emit toxic chemicals in our home. In this article Oliver Style explains what to be on the lookout for, and presents three certification systems that are useful for choosing healthy products and materials.

What does indoor air contain?

To live in a healthy environment, we need to look at the products, materials and furniture we have in our home, since we breathe the particles they emit and we are often in direct physical contact with them.

The first step is to choose paints, varnishes, timber, ceramics, textiles, and furniture with a very low emissions of Volatile Organic Compounds (VOCs). VOCs are of both natural and artificial origin. They all share the common characteristic that they are made of carbon and other elements such as hydrogen, halogens, oxygen, or sulphur. They are present in solids or liquids and are either volatile or occur in a gaseous state at room temperature, which means they move quickly around indoor spaces. Some of them modify the chemical composition of their local environment and are harmful to our health.

Formaldehyde, a colourless, volatile, and toxic gas (classified as carcinogenic by the EU), and other VOCs, are often found in paints, paint strippers, wood preservatives, wood products, binders, glues, waxes, plastics, pesticides, aerosols, synthetic carpets, cleaning products, disinfection products and degreasers. Health effects include asthma, eye, nose and throat irritation, headaches, loss of coordination, nausea, liver, kidney and central nervous system damage. VOCs can be endocrine disruptors and cause respiratory and hormonal diseases, prolonged sleep and behavioural disorders, reproductive disorders and foetal development, cancer, and multiple chemical sensitivity (MCS).

Another harmful component to pay close attention to is particulate matter (PM)- fine particles and fibres with a diameter of 10 micrometres (PM10) or less (PM2.5 and PM 1). PM2.5 particles can reach the lungs, and PM1 can reach the bloodstream. Short and long-term exposure to these particles is associated with cardiovascular and respiratory diseases, including lung cancer. These diseases become more evident when the fibres come from highly toxic materials such as asbestos.

Which are the best materials and products to use in our home?

To avoid and minimize harmful substances inside the home, it’s best to look for products that have been modified or processed as little as possible, made with low-emission paints, varnishes, and glues, formaldehyde free, and if possible, certification for low emissions. Three such certification systems are mentioned below, which classify materials and products and quantify their harmful emissions.

Linoleum or solid wood floors are recommended because they usually contain few adhesives and generally have low emissions. Anything that has been varnished or coated in a controlled factory environment (rather than on-site) will lead to lower emissions in the home. If you use laminated timber flooring, look for one that is free of formaldehyde.

Carpets are in generally not advisable, as they end up collecting all kinds of particles, and in some cases, contain volatile coal ash or polyurethane laminates. Natural fibre carpets are recommended.

Furniture and wood composite products can be a significant source of emissions because they are often made with urea-formaldehyde adhesives. Look for solid wood or plywood furniture, free of formaldehydes. 

As far as kitchen counters go, natural rock is a good option, such as quartz. Alternatively, look for Corian (a synthetic material for solid surfaces composed of acrylic resin and aluminium hydroxide).

As for thermal insulation, exposure to sprayed foam insulation containing isocyanates can cause asthma. If you use fiberglass or mineral wool insulation, make sure it’s formaldehyde free. In general, bio-based or mineral insulation are the healthiest options.

Be careful: products are sometimes sold as “ecological” due to their recycled content, but they can be harmful to your health. For example, some ceramic tiles are made with recycled glass from cathode ray tubes from old TVs, which are considered hazardous waste due to their high lead content.

Emissions & materials: certification systems

1. French certification for indoor air emissions

Emisiones Dans l’air intérieur
Figure 2: Example of the indoor air emissions certification, with A+ product rating

The label “Émissions dans l’air interieur” classifies building materials, furniture and finishing products marketed in France, being mandatory for all products sold there. The certification classifies products according to VOC emissions, from A+ to C (A+ being lowest emissions), according to the ISO 16000 standard. If a product exceeds the limits, it cannot be sold (admittedly “C” class is not very demanding…). The following emissions are evaluated:

  • Formaldehyde
  • Acetaldehydes
  • Toluene
  • Trichloroethylene
  • Xylenes
  • 1, 2, 4 Trimethylbenzene
  • 1, 4 Dichlorobenzene
  • Ethylbenzene
  • 2 Butoxyethanol
  • Estriol

2. Baubiologie Rosenheim Institute certification

Geprüft und empfohlen
Figure 3: IBR Certificate Seal

The IBR, Institute for Biologically Sound Construction, is a German institution that certifies healthy and environmentally sustainable consumer construction products, and includes a series of tests that measure the emissions of a product, including:

  • Radioactivity
  • Biocides
  • Polychlorinated biphenyls
  • Heavy metals
  • VOC
  • Formaldehydes
  • Biological compatibility
  • Electrostatics

3. Eurofins Indoor Air Comfort certification

Eurofins

This certification systems classifies construction products into two categories: Standard level “Indoor Air Comfort – certified product”, which shows compliance with product emissions criteria established by EU authorities, and Higher level “Indoor Air Comfort GOLD – certified product”, which shows additional compliance for product emissions with the criteria set by the most relevant ecolabels and sustainable building organisations in the EU.

MICA Wall indoor air quality sensor
Figure 5: MICA Wall indoor air quality sensor

What you don’t measure you can’t improve

There are several testing laboratories in Spain for the measurement and certification of materials and their VOC emissions, such as Tecnalia, and SGS. What if I want to measure the indoor air quality of my home without spending a fortune? There’s affordable equipment with reasonable accuracy, such as the range of MICA sensors, manufactured by Inbiot. They measure VOC’s, formaldehydes, ozone, suspended particles, radon gas, CO2, temperature and relative humidity.

The following figure shows measured data from a MICA sensor of formaldehyde concentration in a bedroom over the course of a week.

According to the technical standard of measurement in Baubiologie SBM2015 for rest areas, values above 100 μg/m3 are already extremely significant. “The search for emission sources is a bit like looking for a needle in haystack, based on the data and measurements. But you can gradually discard sources until you find the culprit” says Maria Figols, Project Manager at InBiot.

Figure 6: Formaldehyde concentration measured in a bedroom for one week in December 2019

Better living with less emissions

Creating healthy indoor environments is clearly on the agenda, with the construction sector on centre stage. Choosing the right low-emission materials will improve indoor air quality and can help reduce illness for occupants, in the short, medium, and long term. Using products with some of the certification systems shown above is a good place to start. Alongside emissions, these kind of certification systems also assess the environmental impact of a product, making sure they don’t pose a significant hazard during manufacturing, deconstruction, recycling or waste treatment phases.

Acknowledgements

To Maria Figols and Xabi Alaez from InBiot for their contributions.

Bibliography

[1] Guía Edificios y Salud, Siete Llaves para un edificio saludable. García de Frutos, Daniel et al. Consejo General de la Arquitectura Técnica de España, Consejo General de Colegios de Médicos. Enero 2020.

[2] Monitorización de vivienda de alta eficiencia, 30 Marzo 2020. InBiot. https://wiki.inbiot.es/monitorizacion-de-vivienda-de-alta-eficiencia/